The present invention relates to a vial and more particularly to a vial for a carpenter level. Vials are mounted in a carpenter level and comprise a transparent cylindrical tube having an inner hollow cavity. The hollow cavity is sealed at both ends and is filled almost to capacity with a liquid so that a visible bubble remains in the hollow cavity. In order to determine whether a particular surface is level (usually to the horizontal), the carpenter level is placed against the surface. If the bubble within the vial cavity moves to a central position in the vial cavity it indicates that the surface is level. If the bubble moves to one side or the other of the vial cavity center, it indicates that the surface is not level.
Ordinarily vials used for this purpose have a hollow inner cavity which is straight walled and substantially parallel to the outer cylindrical wall of the vial. An undercut is formed in the straight inner cavity into which the bubble lodges in order to give an accurate indication of whether a particular surface is level. Some existing vials are made curved so that the bubble will settle at the apex of the curve if the surface is level but will shift to an area along the edges of the curved vial if the surface is not level.
Since the vials are curved, it is especially difficult to accurately locate them in carpenter levels without precision tools. If for some reason the vials are not precisely located in a carpenter level, the instrument is not accurate. Moreover, it is important for the curved vials and the carpenter levels in which they are mounted to be consistently uniform so that accurate readings are obtained regardless of which particular level is used. These curved vials are often made of soft plastic to facilitate manufacture so that they easily scratch. In addition, existing vials are not always as sensitive as they should be so that their accuracy is compromised.